This invention relates to a unique heater element provided within a motor protection circuit for a scroll compressor motor.
Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor, a first scroll member orbits relative to a second scroll member. Each of the scroll members has a base with a generally spiral wrap extending from its base. The wraps interfit to define compression chambers which are reduced in volume as the two orbit relative to each other.
There are many challenges in the design of scroll compressors. One major challenge relates to a loss of charge in the refrigerant system associated with refrigerant compression. In a loss of charge situation, the amount of refrigerant circulating within the refrigerant cycle is reduced, such as by a leak. Under such conditions, continued operation of the refrigerant cycle is undesirable. Other problems in the system can result in increased temperatures within the compressor. One such problem is so-called reverse-rotation, which can occur such as when a motor is improperly wired such that the system runs in a reverse direction.
Motors for compressors in refrigerant cycles, and in particular for scroll compressors are typically provided with a protector circuit. A motor protector circuit includes a switch which opens should a temperature associated with a protector switch exceed a predetermined maximum. Thus, should the operating temperature within the compressor exceed the expected normal temperature range, the switch will open. When the switch is open, the motor is stopped, thus stopping operation of the compressor.
In one proposed scroll compressor, a thermostat is associated with a location remote from the motor such that it may be positioned closer to the scroll members. The thermostat is operable to move to an actuated position when a predetermined temperature is reached. When the thermostat moves to its actuated position, current flows to a heater position near the motor protector switch. This increases the heat at the motor protector switch resulting in the switch opening at a potentially earlier point in time.
It would be desirable to better utilize the space within the motor protector switch by forming some components to be relatively small and simpler to produce. Moreover, it would be otherwise advantageous to simply the formation of the motor protector switch.
In a disclosed embodiment of this invention, the thermostat preferably communicates with a separate or auxiliary heater. The normal heaters which are typically included in the motor protector circuit operate with a normal function. The thermostat selectively delivers current to an auxiliary heater when closed to shut down operation. This simplifies the motor protector switch wiring.
In another feature of this invention, the heaters are formed by a printed thick film technology. So called xe2x80x9cPTFxe2x80x9d heaters are known, and are formed by printing conductive ink directly on to a substrate. One substrate that can include such heaters are ceramic substrates. Known motor protector devices already incorporate a ceramic insulator inside the protector switch. The inventive heater is thus printed directly on this ceramic insulator. By incorporating the heater into this existing ceramic insulator, less space is necessary, and the resulting protector body is less expensive and more reliable.
In a preferred embodiment the ceramic insulator positioned adjacent to the switch within the protector body receives a PTF or other thin film type heater.